This invention relates to a process for the in-situ production of a blend of polyether polyols, and specifically, a blend of one or more polyether monols and one or more polyether polyols, and to the in-situ formed blend of one or more polyether monols and one or more polyether polyols. It further relates to a process for the production of viscoelastic foams from these blends, and to the resultant viscoelastic foams. The process of the present invention requires a double metal cyanide (DMC) catalyst. The process uniquely employs a monol as the initial starter for epoxidation followed at a later stage in the polymerization by the continuous addition of a polyfunctional starter and continued addition of epoxide to yield a blend of a high equivalent weight polyether monol and a much lower equivalent weight polyether polyol in a single reactor batch. These in-situ formed blends of polyether monols and polyether polyols are suitable for the production of viscoelastic polyurethane foams.
Double metal cyanide (DMC) complexes are highly active catalysts for preparing polyether polyols by epoxide polymerization. Recent improvements have resulted in DMC catalysts that have exceptional activity. See, for example, U.S. Pat. No. 5,470,813.
While DMC catalysts have been known since the 1960s, commercialization of polyols made from these catalysts is a recent phenomenon, and most commercial polyether polyols are still produced with potassium hydroxide. One reason for the delayed commercial availability of DMC polyols is that conventional polyol starters, e.g., water, propylene glycol, glycerin, trimethylolpropane, and the like, initiate DMC-catalyzed epoxide polymerizations sluggishly (if at all), particularly in the typical batch polyol preparation process. Typically, the polyol starter and DMC catalyst are charged to a reactor and heated with a small amount of epoxide, the catalyst becomes active, and the remaining epoxide is added continuously to the reactor to complete the polymerization.
In a typical batch process for making polyols using either KOH or a DMC catalyst, all of the polyol starter is charged initially to the reactor. When KOH is used as the catalyst, it is well understood by those skilled in the art that continuous addition of the starter (usually a low molecular weight polyol such as glycerin or propylene glycol) with the epoxide will produce polyols having broader molecular weight distributions compared with products made by charging all of the starter initially. This is true because the rate of alkoxylation with KOH is substantially independent of polyol molecular weight. If low molecular weight species are constantly being introduced, the molecular weight distribution of the polyalkoxylation products will broaden.
Those skilled in the art have assumed that continuous addition of a starter in a DMC-catalyzed polyol synthesis would also produce polyols having relatively broad molecular weight distributions. Consequently, the DMC polyol synthesis art teaches almost exclusively to charge all of the starter to the reactor initially, and to add the epoxide continuously during the polymerization.
One exception is U.S. Pat. No. 3,404,109. This reference discloses a small-scale process for making a polyether diol using a DMC catalyst and water as a starter. This process describes charging a beverage bottle with DMC catalyst, all of the epoxide to be used, and water, and heating the capped bottle and contents to polymerize the epoxide. U.S. Pat. No. 3,404,109 further discloses that xe2x80x9cwhen large amounts of water are employed to yield low molecular weight telomers, it is preferred to add the water incrementally because large amounts of water decrease the rate of telomerization.xe2x80x9d (See column 7.) Incremental addition of the starter (i.e., water) is used to give a xe2x80x9cpracticalxe2x80x9d rate of reaction. Thus, the ""109 patent charges all of the epoxide to the reactor initially, but adds the starter incrementally.
Interestingly, U.S. Pat. No. 3,404,109 also discloses that incremental addition of water xe2x80x9ccan also be employed to give telomers of a broader molecular weight distribution than those possible where all of the water is added at the beginning of the reaction.xe2x80x9d In other words, the result expected from a DMC-catalyzed process is the same as the result obtained with a KOH-catalyzed process: i.e., the continuous or incremental addition of starter results in polyols with broad molecular weight distributions. Thus, one of ordinary skill in the art upon reading the ""109 patent believes that the incremental addition of a starter to a DMC-catalyzed epoxide polymerization will produce polyols having a broader molecular weight distribution than would be obtained if all of the starter were charged initially.
U.S. Pat. No. 5,114,619 discloses a process for making polyether polyols that involves continuous addition of water and epoxide to a reaction mixture containing a barium or strontium oxide or hydroxide catalyst. A DMC-catalyzed process is not disclosed. The process of the ""619 patent produces polyols with reduced unsaturation. The impact of continuous water addition in the presence of barium or strontium catalysts on polyol molecular weight distribution is not discussed. The ""619 patent further notes that, unlike water, continuous addition of low molecular weight diols, triols, and polyoxyalkylene glycols does not reduce polyol unsaturation. In addition, substitution of KOH for the barium or strontium catalyst does not yield the improvement.
One consequence of charging all of the starter initially, as in a typical batch polyether polyol synthesis, is that reactors must often be used inefficiently. For example, to make a 4000 mol. wt. polyoxypropylene diol (4K diol) from a 2000 mol. wt. polyoxypropylene diol (2K diol) xe2x80x9cstarter,xe2x80x9d the reactor is almost half full at the start of the reaction; to make 50 gallons of product, we would start with 25 gallons of 2K diol starter. A valuable process would overcome such xe2x80x9cbuild ratioxe2x80x9d limitations, and would permit efficient use of reactors regardless of the molecular weight of the starter or the product sought. For example, it would be valuable to have the option to charge our 50 gallon reactor with only 5 gallons of 2K diol starter, and still make 50 gallons of 4K diol product.
In addition to the process challenges of DMC catalysis, commercial acceptance of DMC-catalyzed polyols has been hindered by the variability of polyol processing and performance, particularly in the production of flexible and molded polyurethane foams. DMC-catalyzed polyols usually cannot be xe2x80x9cdropped intoxe2x80x9d foam formulations designed for KOH-catalyzed polyols because the polyols do not process equivalently. DMC-catalyzed polyols often give too much or too little foam stability. Batch-to-batch variability in the polyols makes foam formulating unpredictable. The cause of this unpredictability in foam formulations with DMC-catalyzed polyols has not been well understood, and consistent results have remained elusive.
An improved process for making DMC-catalyzed polyols is described in U.S. Pat. No. 5,777,177. This process eliminates the need to separately synthesize a polyol starter by KOH catalysis, and enables the use of simple starters such as water, propylene glycol, and glycerin. This process also eliminates the problem of reactor fouling by polyol gels, makes efficient use of reactors, and overcomes build-ratio limitations.
While U.S. Pat. No. 5,777,177 discloses the use of an initial starter and the continuous addition of a second starter to produce polyether polyol with a narrow molecular weight distribution, it fails to disclose and/or suggest that this technology can be used to produce in-situ formed blends of polyols of significantly different and relatively narrow molecular weights in a single batch reactor. More specifically, it fails to disclose the in-situ production of a high molecular weight polyether monol and a very low molecular weight polyether polyol as disclosed and claimed in the present specification.
U.S. Pat. No. 5,689,012 discloses a continuous polyol production process which utilizes the continuous addition of one or more starters. However, as in U.S. Pat. No. 5,777,177, the intent of U.S. Pat. No. 5,689,012 is to produce a polyol of a relatively narrow molecular weight distribution. This reference also fails to disclose and/or suggest a process for the in-situ production of a blend of polyols (and particularly a polyether monol and a polyether polyol) having substantially different molecular weights with each component having a relatively narrow molecular weight distribution. It is not apparent from the disclosure of U.S. Pat. No. 5,689,012 that this continuous polyol process can be used for the in-situ production of a high molecular weight polyether monol and a very low molecular weight polyether polyol as described in the present application.
Copending U.S. application Ser. No. 09/495,192, filed on Jan. 31, 2000, which is now U.S. Pat. No. 6,341,935 which is commonly assigned, discloses the production of viscoelastic, slow-recovery polyurethane foams by reacting an isocyanate component, with an isocyanate-reactive component comprising a high equivalent weight monol and a low equivalent weight polyol, at an isocyanate index of at least 90. According to the disclosure of this application, the monol and polyol used as the isocyanate-reactive component are produced in separate reactions, and a single batch process wherein a high molecular weight polyether monol and a low molecular weight polyether polyol are produced in-situ is not disclosed.
U.S. Pat. No. 4,950,695 discloses to use a monofunctional alcohol or polyether to soften flexible polyurethane foams. The formulations also include a 2000 to 6500 molecular weight trio!. Resilience values for the foams are not reported. Accordingly, one of ordinary skill in the art would infer that the foams lack viscoelastic character.
European Patent Application No. 0 913 414 discloses the preparation of viscoelastic polyurethane foams that may contain a polyether monol. The monol, which has a molecular weight less than 1500, is used with a polyol that has a molecular weight greater than 1800. All of the examples show low-index (i.e., less than 90) foams.
Dispersion polyols suitable for the production of hypersoft polyurethane foams are disclosed in U.S. Pat. No. 6,063,309. These polyoxyalkylene dispersion polyols comprise a stable liquid-liquid dispersion of two distinct polyoxyalkylene polyols. The first polyol has a substantial, high polyoxypropylene content internal block and a high polyoxyethylene content external block; and the second polyol consists largely of a high oxyethylene-content block. These compositions form a fine, liquid-liquid dispersion which resists separation and layering and are highly suitable for preparing hypersoft polyurethane foams.
The present invention relates to a unique process wherein DMC catalyzed epoxidation is used to produce a blend of a high equivalent weight monofunctional polyether, i.e., a polyether monol, and a low molecular weight polyfunctional polyether, i.e., a polyether polyol, together (in-situ) in a single reactor batch. This in-situ process eliminates the need for producing, storing, and blending separate polyethers, thus reducing the requirement for multiple tanks and improving production efficiency. Surprisingly, the blend of polyether monol and polyether polyol produced in-situ by this process results in equivalent or superior performance when used in the production of viscoelastic foams when compared to blends made from polyether polyols (i.e., polyether monols and polyether polyols) produced separately.
The invention is a process for the in-situ production of a blend of polyether polyols, and more specifically, a blend of one or more polyether monols and one or more polyether polyols. This invention also relates to in-situ polymerized blends of a polyether monol and a polyether polyol; to a process for the production of a viscoelastic foam by reacting an isocyanate component with an isocyanate-reactive component, wherein a portion of the isocyanate-reactive component comprises the in-situ polymerized blend of a polyether monol and a polyether polyol; and to the resultant viscoelastic foams.
The process comprises the in-situ production of a blend of a polyether monol and a polyether polyol by polymerizing one or more epoxides, in the presence of a double metal cyanide (DMC) catalyst, an initially charged monofunctional starter (Si), and a continuously added polyfunctional starter (Sc). While conventional processes for making DMC-catalyzed polyols and blends of polyols charge all of the starter(s) to be used to the reactor at the start of the polymerization, the process of the invention charges only a monofunctional starter initially (Si) with the DMC catalyst, feeds some epoxide, and allows for reaction between the Si and the epoxide, and uniquely adds both epoxide and one or more polyfunctional starter compounds (Sc) continuously to the reaction mixture during the polymerization.
The process of the invention has surprising and valuable advantages. First, the process provides an efficient route to generate a high equivalent weight monofunctional polyether constituent in the reactor. The DMC catalyst was found to readily initiate epoxidation of the monofunctional starters and the high activity of the catalyst facilitated polymerization to the high equivalent weights required for the intended areas of use. A process involving the more traditional approach of strong base catalysis would require the time consuming steps of dissolving the catalyst in the monol, stripping off excess water and a long reaction time due to the slow epoxidation rate with this class of catalyst. The process would be particularly time consuming for production of monol of equivalent weight greater than about 1,800 due to low reaction rates and the undesired formation of low molecular weight monofunctional starter from isomerization of propylene oxide to allyl alcohol during the base catalyzed process.
Second, the continuous addition of a polyfunctional starter to the preformed polyether monol offers a route to the in-situ generation of a low equivalent weight polyfunctional polyether in the high equivalent weight monol. This is facilitated by the unique ability of the DMC catalyst to promote preferential addition of epoxide monomer to the lowest equivalent weight polyol chains. Surprisingly, by carefully controlling the rate of addition of starter and epoxide, it is possible to produce a low molecular weight polyether polyol having a narrow molecular weight distribution within the higher equivalent weight monol.
Third, the polymerization can be carried out in a sequentially staged single batch process that does not require significantly longer cycle times than a standard single product reaction such as in U.S. Pat. Nos. 5,689,012, 5,777,177, and 5,919,988. The use of an initial starter and the continuous addition of a second starter allows the build ratio to be tailored to the reactor being employed; thus maximizing reactor utilization and production capacity.
Fourth, the in-situ production of the polyether monol and the polyether polyol in a single reactor batch process offers significant efficiency and cost advantages over producing the polyether monol and polyether polyol separately, and then blending the two together. Instead of requiring a storage tank for each of the two components and a third storage tank for the blend, it is only necessary to have a tank for the blend. Also, the inventory is substantially reduced since it is not necessary to maintain the intermediate polyether monol and polyether polyols for blending. In addition, the time and expense of blending products is also eliminated.
Fifth, by controlling the epoxide feed composition in different stages of the reaction it is possible to vary the composition of the polyether monol and polyether polyol in a nearly independent fashion even though they are produced in-situ in a single reactor. For example, propylene oxide may be fed during the polymerization of the polyether monol to yield a low reactivity component and then a mixture of ethylene oxide and propylene oxide may be fed during the continuous addition of the higher functionality starter to produce a more reactive component. Because epoxide adds preferentially to the lower equivalent weight polyether polyol, the polyether monol will remain predominantly poly(oxypropylene) while the polyether polyol can have a relatively high poly(oxyethylene) content.
Finally, it was also unexpectedly found that these in-situ produced blends offer equivalent or superior performance in the production of viscoelastic foams as compared to blends made from polyether monols and polyether polyols which were produced separately.